This invention relates to films which have been widely used in electronic and electric fields, and particularly to poly-paraxylylene useful as an insulating layer of low dielectric constant and high heating resistance between wiring layers, manufacturing method thereof, and semiconductor device using thereof.
The film of this invention means both a freestanding film and a coating film bonded to a substrate, for example an insulating film between wiring layers.
With the development of high-density integration of semiconductor integrated circuits, their wiring line and space have been greatly reduced. As a result, line-to-line parasitic capacitances have become greater and affected the operation speeds of the semiconductor integrated circuits. Various suggestions have been made to solve this problem. One of such suggestions is to use a poly-paraxylylene film of a low dielectric constant as the wiring insulating film.
For example, a poly-paraxylylene film is prepared by subliming 2,2-paracyclophane, which is a cyclophane compound, at 250° C., pyrolyzing the resulting product into the intermediate of paraxylylene at 600° C., polymerizing the intermediate at a maximum of 30° C. in a polymerization tank, and depositing the resulting polymer on a substrate. (K.-U. Buhler, “Heat resistant and thermostable polymers,” Moscow, “Chemistry,” pp. 166-167, 1984.)
Another method of manufacturing poly-paraxylylene, its derivative file, and membrane is disclosed (H. Lee, D. Stoffey, K. Neville, “New Linear Polymers,” Moscow, “Chemistry,” pp. 74-76, 1972). This method comprises the steps of pyrolyzing cyclic poly-paraxylylene dimer (2,2-paracyclophane) and its derivative under a reduced pressure into reactive intermediates, polymerizing and depositing thereof onto substrate surfaces. The pyrolyzing process is carried out in a pyrolyzing tube connected to a polymerizing and depositing chamber. The process further comprises the steps of placing a preset quantity of cyclic poly-paraxylylene dimer or its derivative in a sublimation zone, hermetically closing the container, and reducing the pressure of the container down to 1 to 100 mmHg. Cyclic poly-paraxylylene dimer sublimes at a rate of about 0.25 to 0.35 grams/minute and moves into the sublimation zone. The sublimation zone is kept at 140 to 220° C., although the desired temperature depends upon the monomers used as raw material. The pyrolysis zone is kept at about 600° C. and the decomposed gases are fed to the polymerization chamber which is kept at a room temperature. For some monomer materials, the polymerization chamber is heated up to 160° C. during polymerization.
FIG. 1 shows an example of a manufacturing method for a semiconductor device which uses poly-paraxylylene for the insulating layer. (Japanese Application Patent Laid-open Publication Nos. Hei 09-317499 and Hei 09-345669) A method of producing a semiconductor device having multiple wiring layers comprises the processes of forming a first aluminum wiring 14 on a semiconductor substrate 13, forming an organic polymer layer 15 over the semiconductor device having the aluminum wiring 14 thereon by the above method (Process “a”), forming a silicon oxide layer 16 over the organic polymer layer by a chemical vapor-phase growth (Process “b”), grinding the silicon oxide layer 16 by a chemical machine grinding method (Process “c”), forming via-holes in the layer 15 with tungsten 17, forming a second aluminum wiring on the ground layer 16 (Process “d”), and repeating these processes (a) to (d).
Another process to manufacture multi-layer membranes and films of poly-paraxylylene is provided in U.S. Pat. No. 1,151,546 (1985). This process comprises the steps of pyrolyzing cyclic poly-paraxylylene dimer at 450 to 700° C. under a reduced pressure of 1 to 100 mmHg, depositing the product of decomposition on a substrate at about 15 to 25° C., and polymerizing thereof. Reducing the dielectric constant is desirable for the insulating film of semiconductor devices. Insulating materials having specific inductive capacity of 2.5 or less have been wanted.
MACROMOLECULES 1999,32, 7555-7561 discloses an organic polymer film of a low specific inductive capacity of 2.3 and excellent heat resistance prepared by subliming 1,1,2,2,9,9,10,10-octafluoro-2,2-cyclophane at 70 to 100° C. at a vacuum pressure, pyrolyzing thereof at 650° C., and depositing the resulting polymer onto a cool substrate.